Piezoelectric multiplying device



July 4, 1950 M. K. TAYLOR PIEZOELECTRIC MULTIPLYING DEVICE 2Sheets-Sheet 1 Filed Feb. 25. 1948 0 J) 2 INVENTOQ MAUQ/C'E. K. TAYLOQPM 1 0 3 llolll4 3 $2 1 O Q is 8 5 1- b 2 2 h 2 ATTOQNEY5 J y 4, 1950 M.K. TAYLOR 2,513,899

PIEZOELECTRIC MULTIPLYING DEVICE Filed Feb. 25, 1948 2 Sheets-Sheet 2FIGA.

FIG.5.

I N VENTOR WWQF X74310 ATTORNEYS Patented July 4, 1950 PIEZOELECTRICMULTIPLYING DEVICE Maurice Kenyon Taylor, Eastlothian, Scotland.assignor to Ferranti Limited, Hollinwood, near Oldham, England, aBritish company Application February 25, 1948, Serial No. 10,892 InGreat Britain February 27, 1947 4 Claims.

This invention relates to electrical computing instruments of the typefor obtaining the product 2 of the two known quantities a: and y, inwhich currents or voltages, which may be either al ternating or direct,are derived proportional to the various terms of the computation. Thesecurrents or voltages are hereinafter referred to for convenience as forinstance the :r currents, the a: voltage etc. Such electrical computinginstruments are hereinafter referred to as being of the type stated.

In a known type of such electrical computing instrument the ac and ycurrents are fed into the fixed and moving coils respectively of adynamometer movement, the torque derived in which is thereforeproportional to the product of these currents. When this torque isbalanced by a torque proportional to a third current, e. g. by thetorque set up by a second moving coil carrying this current and free torotate in a fixed field, the third current is proportional to theproduct of the other two and this represents the solution 2 of theequation.

In the above and similar known types of computer a secondelectromagnetic system is required to balance the torque derived fromthe dynamometer and this renders the computer somewhat bulky. Moreoverif the currents fed to the dynamometer coils are alternating (suchcurrents being usually more convenient to deal with) they must be inphase in order to ensure a correct result, thus requiring the provisionof means to ensure this.

The object of the present invention is to provide an electricalcomputing instrument of the type stated in which at least one of the a:and y currents is an alternating current and in which the abovedescribed disadvantages are avoided.

According to the present invention an electrical computing instrument ofthe type stated com- A prises means for deriving an oscillatorymechanical force proportional to the product of the ac and y currents,means for applying said force to one end of a piezo-electric crystal theother end of which is rigidly held so that an alternating voltageproportional to said force is developed between two faces of saidcrystal, and means for deriving the term 2 from the value of saidvoltage or for applying said voltage to a further computer stage.

In the accompanying drawing:

Figure 1 is a diagram illustrating one embodiment of the invention,

Figure 2 is a perspective drawing of part of that embodiment of theinvention illustrated by Figure 1, and

Figure 3 is a diagram illustrating a further embodiment of theinvention.

Fig. 4 is a view similar to Fig. 1 showing a modification.

Fig. 5 is a view similar to Fig. 2 showing a further modification.

In carrying out the invention according to one form by way of example,see Figure 1, an electrical computing instrument of the type statedcomprises a dynamometer movement in which a moving coil I connected toterminals 2 is adapted to vibrate to a limited extent about adiametrical axis in and normal to the field set up by two fixed coils 3,4 connected in series to terminals 5 and wound on the poles 5, l of aferromagnetic field system 8.

The length of the air gap is reduced by a bridge piece 9 offerromagnetic material placed within coil l and secured relative to themain magnetic system 8. Alternatively, the bridge piece may be securedto the moving coil and move with it, though of course this addition tothe mass and hence inertia of the moving member comprising the movingcoil and coil-supporting structure results in a lower value of theresonant frequency of vibration. Moving coil I is secured to one end ofa pieZo-electric crystal l0 responsive to torsion, the other end ofwhich is held against movement by a clamp ll. Electrical connections aremade from the electrodes of the crystal to terminals l2.

In operation, alternating .r and y currents of the same frequency arefed to the fixed and moving coils through terminals 5 and 2respectively.

The oscillatory mechanical force thus set up makes moving coil 1 vibrateabout a diametrical axis normal to the field and thus applies acorresponding oscillatory torque to the free end of crystal Ill which inturn sets up an alternating voltage proportional to the torque, acrossthe faces of crystal Ill connected to terminals [2. The instrument maybe calibrated so that the term 2 may be readily obtained from thisvoltage or the voltage may be applied to a further computer stage.

In another embodiment of the invention as shown in Fig. 4 a fixed andmoving coil system is used as before but the polarity of one fixed coilis reversed so that on energizing the moving coil instead of vibratingabout a diametrical axis vibrates bodily without twisting in the fieldset up by the fixed coils. A corresponding oscillatory force is thusapplied to the free end of a bender crystal the other end of which isclamped.

The resonant frequency of vibration of the moving member may be adjustedin the first of the above embodiments by a simple system of balanceweights. This is illustrated in Figure 2, which shows a coil and crystalmounting arrangement for use with the embodiment illustrated by Figure1, similar parts being similarly referenced; coil I is however now shownwound on the bridge piece 9, which thus acts as the coilsupportingstructure and so forms an integral part of the moving member. Thecrystal is clamped by clamp I to a base member IS. The connections toterminals 2 and I2 are omitted for clarity. Two balance weights M, itare provided; these may be moved by rotation along screwed rods It, i!respectively, projecting from the bridge piece 9 part of the movingmember at right angles to the torsion axis. In the case of the secondembodiment this adjustment may be effected by a weight it (Fig. 5)capable of being moved along screwed rod l9 coaxial with the centralaxis .of the crystal and coil combination. In this case, of course,weights M, 115 with their screwed rods are omitted.

A third embodiment of the invention, see Figure 3, uses twoelectromagnetic systems 29, 26 each of which is similar to that of amoving coil loudspeaker energized by a fixed coil, in the radial fieldset up by which a moving coil may vibrate bodily without twisting, as inthe second of the above described embodiments. The two systems face eachother and between them is located a crystal 2! that is responsive tovarying compressive stress; connections are made from electrodes 22, 23to terminals 24. The crystal is supported at its centre by means notshown and is thus in effect equivalent to two crystals electricallyconnected in parallel and each rigidly held at an end, the two held endsbeing placed back to back at the position occupied by the centre of thecombined crystal. Electromagnetic system has a fixed coil 25 (connectedto terminals 26) wound on the centre limb 2'! of ferromagnetic fieldsystem 28. Moving coil 25 (connected to terminals 36) is wound on analuminium former 3! (having slots, not shown, to avoid eddy currentlosses) secured to one end of crystal 2i and fitting closely but freelyover centre limb 2's. Electromagnetic system 29 is arranged in the samemanner; corresponding parts are accordingly given the same referencenumbers primed. An alternating a: current is fed to fixed coils 25, 25in series or parallel by way of terminals 28, 25 and an alternating 11current to the moving coils 29, 253' in series or r parallel by way ofterminals 3!], 33 In operation, the coils are so connected that theforces set up by these currents subject the crystal to an alternatingcompressive stress proportional to the products of the currents and anoutput voltage proportional to this product is thus set up across thelateral faces of the crystal and is available at terminals 24. In asimilar arrangement a crystal may be subjected to alternating tensionalstress, or alternate tension and compression. In a further arrangementof this embodiment currents proportional to quantities in and q of acomputation are fed to the fixed and moving coils respectively of oneelectromagnetic system whilst currents proportional to quantities r ands of the computation are fed to the other coils.

, The crystal output is in this case proportional to pq-I-rs accordingto the relative polarities.

The output from the above-described embodiments is not affected by anyphase difference there may be between the alternating :1: and ycurrents. Suppose these currents are represented by the generalexpression A sin wt and B sin (wt+) where A and B are the respectiveamplitudes, the periodicity of a common source of supply, it the timefrom the same given moment, and 5 the phase difference between thecurrents. The resulting force is of the form This form is familiar inthe theoretical study of wattmeters and other instruments of thecynamometer type, which are usually designed to respond to the firstpart of the expression but not to the second. It will be observed thatthe first part, (AB/2) cos p, is affected by the phase difierencebetween at and y currents. In electrical computing instruments of thetype stated as hitherto known this phase difference is undesired, sinceif it is not allowed for it may cause incorrect operation, but ishowever not easily eliminated. In instruments'according'to thei'nventionthe force applied to the crystal is proportional to the whole of theexpression (AB/2) cos (AB/ 2) cos (2.wt+) but as the first part, (AB/2)cos qb, merely represents a comparatively fixed distortion of thecrystal the A. C. output from the crystal is unaffected by it, beingrepresented by the waveform (AB/2) cos (Zwt-I-qb) the amplitude of whichvaries only with A or B. The A. 0. output of instruments in accordancewith the invention is thus unaffected by the phase difierence betweenthe currents in the dynamometer section of the computer. An importantadditional advantage is that as the output periodicity is constant at20), the value or" which is usually known, the moving member of thecomputer be made resonant to this value, as described above, and thusdevelop an increased output.

In any of the embodiments one of the two currents may be a directcurrent so long as the other is an alternating current; the outputvoltage is then proportional to the product of the D. C. and A. C.values of the respective currents.

It will readily be appreciated that the use of a crystal enables aconsiderable saving of bulk to be effected. Moreover the fact that themoving coil is attached to a crystal instead of being pivoted onbearings afiords a form of construction which is simple and rigid andwhich does not necessitate the use of ligaments.

A special case of a computer of the type stated is a modulator, fromwhich, as is well known, an output is derived that is proportional tothe product of the carrier and signal inputs. Any of the above-describedembodiments may be used as an eificient modulator.

If resonance of the moving part of the system is not required, forexample, if it is desired to use a wide band of frequencies, the entireinstrument may be immersed in oil so thatresonance is clamped. Thisarrangement has the'additional advantage that the resultant cooling ofthe coils allows a considerable increase in the input wattage.

The above-described embodiments are for illustration only and by nomeans exhaust the scope of the invention. In this connection it shouldbe understood that the term computer should be constructed in a widesense to include all means whereby an output voltage proportional to theproduct of two input currents is obtained.

I claim:

1. An electrical computing instrument of the type for obtaining theproduct 2 of two known quantities as and y comprising means forsupplying two electrical currents proportional to the quantities :a andg respectively, means for derlving an oscillatory mechanical forceproportional to the products of the a: and y currents, a piezo-electriccrystal, means rigidly holding one end of said crystal, a mechanicalconnection for applying said mechanical force to the other end of saidcrystal so that an alternating voltage proportional to said force isdeveloped between two faces of said crystal, and means for deriving theterm 2 from the value of said alternating voltage.

2. An electrical computin instrument of the type for obtaining theproduct 2 of two known quantities a: and y comprising means for.supplying two electrical currents proportional to the quantities a: andy respectively, means for deriving an oscillatory mechanical forceproportional to the products of the a: and y currents, including adynamometer movement having fixed and moving coils whose axes are atapproximately right angles to each other and means for feeding the a:current to one of said coils and the y current to the other of saidcoils so that in operation said force causes said moving coil to vibrateabout a diametrical axis thereof in the field set up by said fixed coiland normal to said field, a piezo-electric crystal, means rigidlyholding one end of said crystal, at mechanical connection for applyingsaid mechanical force to the other end of said crystal so that analternating voltage proportional to said force is developed between twofaces of said crystal, and means for deriving the term a from the valueof said alternating voltage.

3. An electrical computing instrument of the type for obtaining theproduct a of two known quantities a: and y comprisin means for supplyingtwo electrical currents proportional to the quantities a: and yrespectively, means for deriving an oscillatory mechanical forceproportional to the product of the a: and y currents, including fixedand moving coaxial coils and means for feeding the a: current to one ofsaid coils and the y current to the other or" said coils so that inoperation said force causes said moving coil to vibrate bodily withouttwisting in the field set up by said fixed coil, a piezo-electriccrystal, means rigidly holding one end of said crystal, a mechanicalconnection for applying said mechanical force to the other end of saidcrystal so that an alternating voltage proportional to said force isdeveloped between two faces of said crystal, and means for deriving theterm 2 from the value of said alternating voltage.

4. An electrical computing instrument of the type for obtaining theproduct 2 of two known quantities a: and 1/ comprisin means forsupplying two electrical currents proportional to the quantities a: andg respectively, means for deriving an oscillatory mechanical forceproportional to the product of the a; and y currents, including fixedand moving coils and means for feeding the a: current to one of saidcoils and the 1/ current to the other of said coils so that in operationsaid force causes said moving coil to vibrate bodily without twisting inthe field set up by said fixed coil, a piezo-electric crystal, meansrigidly holding one end of said crystal, a mechanical connection forapplying said mechanical force to the other end of said crystal so thatan alternating voltage proportional to said force is developed betweentwo faces of said crystal, and means for derivin the term 2 from thevalue of said alternating voltage.

MAURICE KENYON TAYLOR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,289,183 Ehret July 7, 19422,401,527 Vance June 4, 1946

